1. Field of the Invention
The present invention relates to a steel cannula for spinal and peridural anaesthesia, and in particular a steel cannula comprising a straight tube whose front end includes an atraumatically pointed rotationally symmetric tip and an elongated lateral opening of the tube channel provided behind the tip.
2. Description of Related Art
The use of cannulas having a ground surface with a cutting or tearing property may be accompanied by injuries of vessels, dura and nerves in the case of spinal or peridural anaesthesia. Above all, bleeding in the peridural space, postspinal headaches and temporary to persistent neuronal losses of function may occur.
A known steel cannula for spinal and peridural anaesthesia consists of a rectilinear tube having a pointed front end. Immediately behind the top portion, a lateral elongated opening is ground into the cannula wall to extend as far as possible to the center axis of the cannula and to merge edgelessly with its front and rear border into the top portion or the external jacket surface of the cannula. The tube channel extends beyond the front end of the opening as far as into the top portion. Such a steel cannula causes a slight atraumatic puncture hole, because the point separates the longitudinal fibers of the dura and it does not cut through them. Such a steel cannula is not suitable for positioning a catheter, but only for directly injecting anaesthetic through the cannula channel. As compared to the rigid steel cannula, a flexible catheter is more advantageous for injecting anesthetics and drugs because of its longer service life. Moreover, it may be left in the body upon the removal of the cannula used for its application.
There has also been known a double cannula (German OS No. 32 18 242) having a sharp open point and an inner cannula whose blunt tip is closed and round. From an opening provided laterally behind the blunt tip, a catheter which is introduced through the inner cannula is adapted to be guided out through an oblique guide surface. The disadvantages involved with said double cannula reside in the great expenditure concerning puncture cannula and inner cannula, the complicated techniques for applying the catheter, and the intensive bleeding in the epidural space caused by the blunt tip.
It is an object of the present invention to provide a one-piece cannula which may be applied in one move and which is adapted to safely position a catheter.